(a) Field of the Invention
The present invention relates to a system and a method for a driving mode conversion of a hybrid vehicle, and more particularly, to a system and method for a driving mode conversion that prevent an unnecessary engine on/off and improve drivability and fuel efficiency by predicting a near future driving intention of a driver taking account of a driving environment of the vehicle and a propensity of the driver, and utilize the predicted near future driving intention of the driver to determine whether an engine is started.
(b) Description of the Related Art
In general, in accordance with the constant demand for an improvement of fuel efficiency of a vehicle and the tightening of exhaust gas regulations, the demand for an environmentally-friendly vehicle has increased. As a practical alternative thereof, a hybrid electric vehicle and a plug-in hybrid electric vehicle (HEV/PHEV) have been developed. The hybrid vehicle may provide optimal output torque based on how an engine and a motor are harmoniously operated in a process in which the hybrid vehicle is driven using two power sources consisting of the engine and the motor. In other words, as a driving mode of the hybrid vehicle, an electric vehicle (EV) mode by electric power, and an HEV mode that drives the vehicle using two or more powers such as the engine, the electric power, and the like are applied. In addition, in the hybrid vehicle, the determination of a conversion point of time of an EV/HEV mode is a factor in improving drivability and fuel efficiency of the vehicle.
Meanwhile, a driving mode conversion method of a hybrid vehicle according to the related art and a disadvantage thereof will be described with reference to FIGS. 1 and 2. FIG. 1 is a graph illustrating an EV/HEV mode determination reference in a hybrid vehicle according to the related art. Referring to FIG. 1, a typical engine on/off control in the hybrid vehicle includes a state of charge (SOC) of a battery, a warm up of an engine, a required power condition of a driver, and the like, and a turn on/off of the engine is basically at proper required power by system driving efficiency.
FIGS. 2 and 3 are graphs illustrating engine off and engine on occurrences according to an intermittent change in required power according to the related art. Referring to FIG. 2, an engine off due to an intermittent accelerator tip out (APS Tip out) occurs during a high speed and fixed speed driving of the hybrid vehicle. Further, referring to FIG. 3, an engine starting (ON) due to an intermittent accelerator tip in (APS Tip in) occurs during a low speed driving of the hybrid vehicle in a parking lot or a congested area. Accordingly, since power for cranking during engine on/off according to the intermittent change in the required power and additional fuel for the engine starting are used, it is disadvantageous for the fuel efficiency, and since drivability is deteriorated due to a frequent engine on/off, an unnecessary engine starting should be avoided.
In addition, FIG. 4 is a graph illustrating a time delay between an engine on determination point of time and an engine on completion point of time according to the related art. Referring to FIG. 4, it illustrates the time delay between the engine on determination point of time and an actual engine starting completion point of time in an environment to which the intermittent change in the required power of the driver is input. In particular, since the required power exceeds a threshold at the engine on determination point of time, the HEV mode is efficient. However, since the required power is decreased below the threshold at the engine starting completion point of time, the HEV mode may be inefficient. In other words, an inefficient driving occurs due to the time delay between the engine on/off determination point of time and the engine on/off completion point of time in a driving environment to which the intermittent change in the required power of the driver is input, and thus is disadvantageous in view of the system efficiency such as the fuel efficiency, the drivability, and the like.
The above information disclosed in this section is merely for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.